this is the problem, comparing apples & oranges. i really wish someone would post sound levels for everything. THAT is my highest priority, keeping my neighbors out of the loop. i had a reasonably quiet hobo setup using a generic box fan with a cheap furnace filter/carbon scrubber behind it blowing air into a cardboard funnel i made blowing into my light & pushing air out of the room when i opened the door at night and continually scrubbing the room's air in the daytime too. i'm sure i wasn't moving a lot of air as you could just feel a gentle breeze blowing out of the exhaust. i didn't have any duct howling problems, but my next rig is going to have two lights and a better DIY carbon scrubber. the hobo system though was quiet enough that i had to be in the room to hear it even with the duct blowing out of the room and it moved enough air that my single 400w light was merely warm to the touch on top.
these fans get really expensive. is there anyplace that tests fans & speed controller combos? you'd think with all of the indoor gardening, high times or someone would do a shootout & measure noise with an SPL meter.
kudos on the "self cooling" info on fans. i wasn't aware of that and worried about heating problems if i were to make a soundproofing box for a fan. odor shouldn't be the biggest concern for my grow as i don't do funky strains, but i like to keep EVERYTHING low profile.
i don't know that i can afford $250 or so for that panasonic. i'm thinking of maybe just getting a 4 inch value line and a speed controller. i just want to move enough air to keep my lights cool and do some scrubbing without making a lot of racket or breaking the bank.
things get even more complicated when you toss in cheaper squirrel cage fans that you can't put a speed controller on & there just isn't any info on this online. i really wish someone would do a fan shootout comparing various brands, sizes & types & factoring in speed controllers to come up with a DEFINITIVE "quietest fan setup in the world".
i bet the reason the panasonic is so quiet is that it has it's own case, but i bet you could get even quieter with some thick wood around a regular inline as that would dampen vibrations better than sheet metal.
hey... THERE'S an idea... if your inline fan's case is humming, try sticking some of that dynamat used for carsound competitions on it to dampen vibrations a little.
all the descriptions of ALL duct fans make them sound louder than a big old box fan on low even if they don't have the same pressure capabilities. keeping it quiet is way more important than how many cubic feet per minute a fan moves for me. low odor strains do most of the carbon scrubbing for themselves. i really don't want to invest way more money than i even want to spend on something i might not even end up using. this is so frustrating not getting solid answers and only getting discouraged that fans might cause more problems than they solve.